Patent GB-540931-A (GB)
Title: Improvements in or relating to a photographic colour printer
IPC: G03B27/73
Filed: 1940-12-31
Abstract: 540,931. Photographic projection printers; colour photography. KODAK, Ltd. (Eastman Kodak Co.). Dec. 31, 1940, No. 18236. [Classes 98 (i) and 98 (ii)] In making a colour print on photographic sensitive material from a transparency, the colour balance of the transparency is judged by forming an image of it on a viewing screen and illuminating the border of the image area with substantially white light to facilitate judgment of deviations from the correct balance, which are then corrected by inserting removable filters in the printing light. A projection printing apparatus for carrying out the method comprises a source of illumination and an optical system including an objective for forming an image of the transparency, a mirror capable of being removably positioned between the objective and the printing plane to reflect the image on to a viewing screen, a source of light to illuminate the borders of the screen around the image, and colour filters which may be inserted in the printing light beam to correct the colour balance. The apparatus described comprises also automatic focusing means adjusting the positions of a horizontal transparency gate and a vertical printing gate, automatically adjusted masking means at both gates, and motor-operated means for winding on the printing paper, the length wound being automatically adjusted in accordance with the length of the exposure aperture as determined by the masking. As shown, the light path from a printing lamp 1 to the printing paper 2 includes a condenser 3, relay lens 4, and a reflector 5, which reflects the beam upwards through a field lens 6 and transparency gate 11 to a second reflector 7 which deflects it through an objective 8 to the exposure aperture 20, all of these optical elements being carried by a housing 9. The objective 8 being fixed, automatic focusing is performed by vertical movement of the gate 11 in which the transparency is held and corresponding horizontal movement of the compartment 18 in which the printing paper is carried. For this purpose the gate 11 is mounted in a carrier 12 vertically slidable in a housing 13 carried by the front wall of the apparatus, and the compartment 18 is mounted on the rear wall of a chamber 10 supported by rollers 21 in horizontal tracks 22. The movements of the carrier 12 and chamber 10 are correlated to maintain correct focus by a pair of levers 23 pivoted at 24 to the housing having grooves and engaging studs 27, 28 secured to the carrier and chamber 10, the geometry of this construction being explained in the Specification. The width of the image on the printing paper is kept constant for all degrees of enlargement, being determined by the height of three exposure apertures 19 in the front wall of the compartment 18 extending across the width of the printing paper. These apertures are selectively brought into printing position opposite a corresponding aperture 20 in the rear wall of the chamber 10 by vertical movement of the compartment 18, for which purpose the latter is carried by a plate 72 which is vertically adjustable on the chamber 10 by means of rack and pinion gears 96, 97, Fig. 13, operated by a motor 93. The transparency gate is provided with masks 39, which are automatically adjusted as the enlargement ratio is changed so that the width of the gate corresponds to the width of the image opening 19, for which purpose the masks are carried by numbers engaging oppositely-threaded portions of a shaft 42 carrying a pinion 44 in engagement with a fixed rack 45, so that vertical movement of the gate causes rotation of the shaft and consequent movement of the masks. The length of the transparency gate is simultaneously adjusted by masks 46, one only of which is shown, controlling the length of the gate. As the gate is raised or lowered a rack 51 carrying a pin engaging one of a pair of inclined slotted arms 47 is thereby moved longitudinally, so rotating through a pinion a shaft 53 carrying a further pinion engaging a rack 55 on the mask 46, which is thereby moved. To change the proportions of the picture the lengths of the transparency gate and the printing gate are simultaneously adjusted by rotation of a shaft 64. This causes rotation of a shaft 60 having a pair of oppositely-threaded portions 61 each engaged by a block 62 carrying a stud engaging one of the grooved arms 47, which are oivoted at their upper ends. The inclination of these arms is thus varied, so adjusting the masks 46. The corresponding adjustment of the length of the printing gate is effected by horizontal movement of a plate 71 which carries the compartment 18 and is formed with a ridge 76, Fig. 8, defining one vertical edge of the gate opening, and by opposite movement of a mask plate 77 carried on it and forming the opposite edge. For this purpose the plate 71 is carried by horizontal slides on the plate 72, and carries a nut 74 engaged by a threaded shaft 70 rotated through bevel gears and a vertical shaft 67 from the shaft 64. A pair of levers 78 pivoted at 79 to the plate 72 and having slotted ends engaging studs 80, 81 on the plate 71 and the mask plate 77 give the latter a movement opposite to that of the plate 71. To facilitate the masking operations, the transparency in the gate 11 may be examined through an eye-piece 99 by raising the pivoted reflector 7 to the upper position shown in broken lines. To detect discrepancies in the colour balance of the transparency a viewing chamber 103, carried by rollers 105 engaging in tracks 104, is moved into the path of the light from the objective 8 by means of a rack 109, Fig. 13, carried by it and engaging a motordriven pinion 107. The image formed by the objective, diminished in size by a lens 111 in the front of the chamber 103, is then thrown by a reflector 112 on to a screen 113, above which is a reflector 114 enabling the image to be viewed through the eye-piece 99. At the bottom of the chamber 103 is a lamp 116, light from which is reflected to the borders of the screen 113 by a pyramidal reflector 117, but is prevented by baffles 118 from falling on the image area. The illuminated border enables discrepancies in the colour balance to be readily detected and to be corrected by means of filters 119 pivotally mounted so that they may be brought into the beam from the lamp 1 by operating Bowden controls connected to them. Variations in the colour of the light from the lamp 1 also affecting the colour balance of the image are simultaneously corrected. Variations in the colour sensitivity of the printing paper are also corrected by use of the filters 119 or, if these do not cover a sufficient range, by a separate filter 131. If the filter 131 is not removable, a filter 130 of the same spectral transmission is positioned between the lamp 116 and the viewing screen 130 in order that the border comparison light may be correspondingly corrected. The filters 130, 131 are preselected by sensitometric tests of the paper. A rotary density wedge 125, operated by a flexible shaft, allows the intensity of the image to be varied for convenience in colour comparison and to allow the use of a constant exposure, the illuminated border of the screen 113 serving as a comparison photometer. The exposure is made by a rotary shutter 132, which is preferably electrically operated. The printing paper is fed from a supply roll 14 and over a roll, at each side of the printing gate, one only of which is shown at 16, to a take-up roll not shown. The feeding is performed by a motor-driven shaft 138, Fig. 16, which through a friction clutch 142 rotates a vertical shaft 140 carrying a plate 143 having apertures in which engage studs extending from the roller at one side of the gate. The take-up roller is similarly driven by a plate 165 carried by a shaft 166 driven through a slipping spring clutch 167. When the winding is completed, a contact 153 carried by a disc 154 rotating with the clutch 142 engages and bridges contacts 155, so energizing a solenoid 152, which then opens a switch 147 and de-energizes a solenoid 146. A rod 145 connected to the core of this solenoid is then retracted by a spring, opening a switch 144 in the motor circuit and lowering clutch arms 150 to disengage the clutch 142, thus stopping the paper feed. A spring 158 then rotates the disc 154 until the bridging contact 153 reaches its initial position against a fixed stop 157. When the length of the printing gate is adjusted, the lateral movement of the compartment 18 causes rotation of a pinion 163 in engagement with a rack 162 carried by the plate 72 and also with a pinion 161 to which is secured an arm 160 carrying the contacts 155. The angular position of the contacts, and hence the length of the paper wound, is thereby adjusted in accordance with the length of the printing gate. To rewind the paper, a plate 143 and 165 are lowered out of engagement with the studs on the rollers by a solenoid 173, which lowers arms 170 by which the plates are held in the raised position. The supply roll is then driven by a motor 176 through a clutch 178, Fig. 2. Specifications 540,934 and 540,935 are referred to.